This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is a Phase I dose-finding study with objectives to show that a whole food extract of white button mushrooms (WBM) can inhibit aromatase-induced estrogen biosynthesis in postmenopausal breast cancer survivors (BCS), and to determine the optimal daily dose to induce this effect;and to determine the bioavailability of C-18 unsaturated fatty acids (CUFA), which are thought to moderate the anti-cancer effects of WBM. The secondary objectives of this study are to determine safety and tolerability of WBM in humans via serial comprehensive symptom questionnaires, pre- and post-treatment markers of bone metabolism, and pre- and post- treatment comprehensive lipid panels. To explore potential alternate anti- tumor mechanisms, specifically the effect of WBM on cytokines as well as innate and adaptive cellular immunity;and to describe barriers experienced in recruitment of ethnically diverse subjects from the community into a secondary prevention trial BCS utilizing a dietary supplement intervention, in an effort to enhance feasibility of a subsequent Phase II trial.